Nokia has admitted that some customers are seeing BP-6M batteries, as used in the N73 handset, ballooning to several times their original size, and in some cases to such an extent that the phone case won't close.
El Reg first heard about the problem from a reader just after Christmas, and Nokia has been investigating since. Today the company assures us that the issue is nothing to be concerned about, and customers who find their batteries bulging should nip down to their nearest service centre for a free replacement.
Be sure you've got a real Nokia, though - the company won't take responsibility for fakes and has a website where you can check, and find out the location of your nearest service centre if you do have a pukka powerpack.
Lithium-ion batteries often gently swell up after a few years, and even unused batteries tend to enlarge after around three years, so those unused handsets you stuck in a drawer could be popping open as you read this. Not that there's any risk from this - it just makes the batteries hard to fit into the charger, or mobile phone, and shouldn't happen for a few years at least.
Nokia isn't saying how common the problem is, only that it affects a "limited number of batteries" and that the swelling presents "no risk to health of safety" - assuming of course that your health and safely doesn't depend on having a working telephone before you have a chance to switch batteries. ®